THE new TNS poll is an unmitigated disaster for Labour. At 32 points, the SNP’s lead is bigger than any firm has reported since the independence referendum, and is far beyond the level at which tactical voting can be expected to eat into the impending landslide.

The only consolation for Jim Murphy lies in what the poll cannot tell us, rather than what it can. Because of the unique face-to-face methods TNS uses, its findings are often already somewhat out of date by the time of publication, and that’s the case here – the fieldwork for the poll started way back at the start of April, and concluded as long ago as the 19th. In theory, this obviously leaves open the possibility that the SNP surge may have gone into reverse since then. Unfortunately for Labour, though, we already have a Panelbase poll conducted at the start of last week that showed the SNP lead soaring to a record-breaking level.

A more realistic area of uncertainty that can be identified is the substantial chunk of the electorate that has yet to decide how to vote.

Some 29 per cent of respondents who told TNS they are certain to vote haven’t made up their minds yet, which is exactly the same number as in the last poll by the same firm.

That’s an important finding, which leaves some scope for a late Labour fightback. However, we shouldn’t jump to the conclusion that it means the contest somehow remains wide open. In any election, there are voters who will not make their choice until the very last minute. If this was a routine Westminster campaign in which Labour were coasting to victory in Scotland, we certainly wouldn’t look at the large number of "don’t knows" and assume the SNP still had every chance of turning things around. The situation isn’t necessarily more volatile simply because a different party holds the lead.

Yes, it’s sometimes true that undecided voters break in a surprising way. But they are influenced by the same political climate as everyone else, and the current climate is one in which the SNP are utterly dominant. In any case, people who still haven’t chosen a party are probably less likely to turn out next Thursday, regardless of how highly they rate their chances of getting to a booth when quizzed by a polling firm.

We can’t even take it as read that TNS is correctly estimating the number of undecideds. During the referendum, it gained a reputation for reporting far more "don’t knows" than any other firm, and that pattern has continued since.

To imagine that Labour can make telling inroads before polling day, Jim Murphy must put his faith in the following possibilities: that TNS is closest to the truth about the scale of indecision, that "don’t knows" will care enough to turn out to vote in substantial numbers, and that they will break dramatically against the prevailing tide. A prayer mat may come in handy during the days to come.